Learn Croatian: Bio sam propustio presjedanje. - I had missed the connection.

The pluperfect (past perfect) translates to "had missed". It is made by taking the standard perfect tense of the verb biti (to be) — which in this case is bio sam (I was) — and adding the past action word (l-participle) of the main verb, propustio (missed).

Why is the word sam placed between bio and propustio?

Sam is an enclitic, meaning it's an unstressed word that strongly prefers the second position in a sentence. Here, it naturally falls right after the first word, bio, splitting up the two main parts of the pluperfect structure (bio and propustio).

How do we know the speaker of this sentence is male?

We can tell because both past action words (l-participles), bio and propustio, end in -o, which is the masculine singular ending. If a woman were speaking, she would use the feminine -a ending for both and say: Bila sam propustila presjedanje.

What case is the word presjedanje, and why does it look exactly like its dictionary form?

It is in the accusative case because it's the direct object of the verb (the thing that was missed). Presjedanje is a neuter noun, and for all neuter nouns, the accusative case form is identical to the nominative (dictionary) form.